Media captionThe BBC's David Loyn reports on the growth of IS in Afghanistan

The first concrete evidence has emerged of attempts to recruit fighters in Afghanistan for the so-called Islamic State (IS).

A former Taliban commander in Helmand province, Mullah Abdul Rauf, has declared his allegiance to IS.

An elder from the Sangin district, Sayeduddin Sanginwal, told the BBC that the new group had fought with the Taliban after replacing white Taliban flags with the black flags of IS.

He said about 20 people from both sides had been killed and injured.

The deputy commander of the Afghan army unit responsible for the area, General Mahmood, confirmed that he had received reports of the new group within the past few days.

He said they were trying to win support for the IS cause, and they were "preparing to fight".

The leader of the new movement, Mullah Abdul Rauf, was a former senior Taliban commander who spent six years in Guantanamo Bay after being captured by US forces in 2001.

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Video has emerged showing several Afghan commanders said to be backing Islamic State

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The Afghan Taliban leader, Mullah Omar, has not been seen in public in years

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Some of his followers have reportedly shifted allegiance to the IS leader, Abu Bakr al-Baghdadi

There had been reports that he had fallen out with the leader of the movement Mullah Omar.

'Same people, same programmes'

Rauf is a distant relative of the Governor of Nimruz province, Amir Mohammed, who said that the commander had lost a leg before being taken to Guantanamo.

The governor said that IS had already attempted to recruit people in Farah, another south-western province, but had been driven out by local people with the help of the police.

He said they were all the same: "Once they fought under al-Qaeda name, then as Taliban, and now IS, they are the same people with the same programmes."

In another sign that the Taliban are facing internal challenges, a former spokesman for the Pakistani Taliban has appeared in a video online, saying that there were several IS commanders operating, and that the Pakistani Taliban were now allied to the movement.

There is no independent verification of this claim, but the video had images of several commanders across Afghanistan who were also said to be now backing IS.

In the video they claim to have shifted their allegiance from the Taliban leader, Mullah Omar, to the IS leader, Abu Bakr al-Baghdadi.

This represents the first serious challenge to the coherence of the Taliban leadership for many years.

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Elders who have seen years of civil war are aghast to see the rise of Islamic State

Omar has not been seen in public since 2001.

His fighters have continued their assault on Afghan military targets, even after the end of foreign combat operations at the end of 2014. And despite sustaining very heavy casualties, particularly among the police, Afghan forces have held their ground.

New group emerging?

A major ceremonial event has been held in the headquarters of the military garrison in Helmand province to tell political leaders that the Afghan forces are now in control.

Huge areas of the base, called Camp Bastion by British forces, are now deserted as Afghan forces occupy only a small part of it.

Commanders say that the fighting season has gone on through an unseasonably dry and mild winter in Afghanistan - but if IS does succeed in infiltrating Afghanistan, the nature of the war will change.

Elders who came into the base to witness the show of military strength said that they had seen the Russians come and go, and now the British and Americans, but they hoped that Islamic State would not come.

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Afghan forces have now assumed control of the Camp Bastion military base

There are also accounts that a group called Khorasan has been attempting to recruit fighters in Wardak province.

Khorasan is an old name for Afghanistan, and is a word that carried mythical overtones for some Muslims after an ancient prophecy that black flags would once again fly in Khorasan before the end of the world.

The US said that an air strike near Aleppo in Syria last September was on a base used by a previously unknown group also called Khorasan.

This group was allied to Islamic State, but it is not clear if there is any connection with the attempts to win support for Khorasan in Afghanistan.

This all appears to mean that the Afghan conflict is entering a new and unstable phase.

There have been more direct suicide attacks recently on civilians - including a volleyball game - which had not been Taliban targets in the past.

If Mullah Omar is losing his grip and Islamic State has infiltrated the country, then it will represent the biggest challenge yet to the new government of President Ashraf Ghani, who has only now announced a cabinet after more than three months in office.